Diacrylate compositions, heat resistant polymers containing the same and method of making electrical laminates therefrom



United States Patent ice 39mm Patented Mar. 12, 1968 3 373 075 are eliminated in the formation of beta-hydroxy car- DIACRYLATE COMIQOSITIONS HEAT RESISL boxyhc esters with the carboxylic acid:

ANT POLYMERS CDNTAlNlNG THE SAME O o 0 AND METHOD OF MAKING ELECTRICAL LAMNATES 'IHEREFROM 5 -0monorn o -omonomoo Frank Fekete, Monroeville, Patrick J. Keenan, Pittsburgh, 5

and William J. Plant, Monroeville, Pa., assignors to Roberison p y: Pittsburgh, -a a 'l ora- The present diacrylates are readily homopolymerizable tion of Pennsylvania No Drawing. Continuation-impart of abandoned application Ser. No. 160,247, Dec. 18, 1961. This application in the presence of familiar addition polymerization initiators such as the peroxy compounds which are well known as initiators of the polymerization of C=CH 6} 331106 radicals. These present diacrylates are also readily co- -alms. (Cl. 161-185) polymerizable With monomers which contain at least one This application is a continuation-in-part of copending t i l CZCH di l f example, styrene, i yl patent application Ser. No. 160,247 filed Dec. 18, 1961, toluene, divinyl benzene, dialiyl phthalate, triallyl cynow abandoned. an'urate, methyl methacrylate, ethyl methacrylate, methyl This invention relates to heat resistant solid cured theracrylate, ethyl acrylate, ethylene glycol dimethacrylate, moset resinous compositions, fibrous reinforced articles beta-hydroxy ethyl methacrylate, beta-hydroxy propyl embodying the compositions adapted for use at elevated methacrylate, and other ones of the diacrylates 0f the temperatures, to curable thennosetting resinous compo- 20 general type under discussion, and the like. sitions for preparing the same including fibrous reintorc- The resinous compositions may be used alone or with ing elements and curable thermosetting resinous comfiller substances such as calcium carbonate, mica, silica positions, and to a process for preparing heat resistant and the like as casting or encapsulating resins. However articles comprising cured thermoset resinous components. these present materials are of especial interest in com- The present solid thermoset resinous compositions are bination with fibrous reinforcing materials such as glass of especial interest in electrical laminate sheets, in elecfibers, glass filaments, woven glass fiber fabrics, glass trical armature slot sticks, in electrical banding tapes, in fiber mats, glass fiber roving and bundles, and other pre-pregs and pre-mixes. fibrous materials which might be utilized as reinforcing fibers. STATEMENT OF INVENTION The cured thermoset resinous articles of this invention According to this invention, thefmosetting resinous resist softening and loss of strength at elevated temperacompositions are provided which comprise as essential tures i th range of 150 t 500 F, L i th n r l e tain diacrylates having the formula temperature range of Class H electrical insulating ma- 0 O CHz=CiiOCHrCHCHzOQCO[CH2CHCH2OCO-h-CHqCHCH OiC=CHs i (if! i ()H 1: (CH3): (CH3)! wherein R is a substituent selected from he cla s 0 11- terials as established by the American Institute of Elecs i g of y g methyl and ethyl radicals a d n is trical Engineers. The present materials provide a relaan integer from Zero Y- These diacfylates y 40 tively inexpensive thermoset resinous composition which be homopolymel'iled of y be 0P01YmefiZ6d Wi not only retains its physical strength at elevated temperapolymerizable monomers having at least one t n l tures, but also retains its dielectric values and further a radical such copolymefl'zable monomers resists deterioration from many common solvents and clude Viny COHIPOIIHdS, rylic compounds and allyl comchemicals at these elevated temperatures. Deliberate postpounds, for example. The diacrylates are prepared pref- 4:5 cure heating steps improve the resistance of these cured erably by reaction of a diglycidyl ether or polyglycidyl thermoset articles to subsequent thermal exposure. ethers of Bisphenol-A with two mols of a carboxylic acid OBJECTS selected from the class consisting of acrylic, methacrylic and ethylacrylic acid. The principal objects of this invention include:

The polyglycidyl ethers of Bisphenol-A have the fol- To provide thermal resistant articles of thermoset reslowing general formula inous compositions, especially those which will retain sub- 0 O\ C H2 OHCH2OCO[CH2CHCH2OOO-]aOH HCHg I ta l (CH3): (CH3):

wherein n is an integer from zero to twenty. In the instantial physical strength at elevated temperatures bestance wherein 1: equals zero, the material is the diglyc tween about 150 and 500 F. and after exposure to such idyl ether of Bisphenol-A temperatures;

0 0 To provide fiber-reinforced thermoset articles which E retain substantial structural strength and dielectric values CH'CHCHO during and after exposure to elevated temperatures;

i To provide electrical laminates and castings which are (0113) r useful at elevated temperatures; The reaction between the polyglycidyl ethers of Bis- To provide thermoset articles which are resistant to phenol-A and the carboxylic acid proceeds readily in the deterioration from many common solvents and chemicals; presence of triethylamine as a catalyst at relatively low To provide uncured resinous-coated fibrous substances temperatures. The two reactants are maintained at reacwhich are useful in preparing resinous articles, such as tive conditions until substantially all of the epoxy groups 7 0 banding tapes, pre-pregs and the like;

3 To provide homopolymers and copolymers of diacrylates of polyglycidyl ethers of Bisphenol-A which have been post-cure heated to achieve remarkable resistance to thermal deterioration.

DIACRYLATES The diacrylates which are the essence of this invention are preferably formed by reaction between a polyglycidyl ether of Bisphenol-A having the formula 4 n or the identification of R is different from that of the principal ingredient.

COPOLYMERS-PROPORTIONS The present diacrylates comprise from 95 to 50 weight percent of the copolymerizable resinous compositions of this invention with one or more copolymerizable monomers comprising from about 5 to 50 weight percent of the resinous composition. For each selected copolymorkznomoQcn-omonomoooqromdnom l t wherein n is an integer from zero to twenty; and a mono- 1 carboxylic acid possessing ethylenic unsaturation and having the formula 0 Clix- 00 It OH the diacrylate will be an integer. Nevertheless, the average value of n for a typical diacrylate will only seldom be an integer for the reason that a spectra of values of n normally is presented according to the composition of the polyglycidyl ether of Bisphenol-A which is selected. In the general use of the above formula, therefore, the designation of the value of it refers to its average value whereby the composition will include materials having actual nvalues above and below the designated value (except, of course, in the case wherein n is zero).

Where It is zero, the desired diacrylate may be formed alternatively by reaction of two mols of the glycidyl ester of a monocarboxylic acid 0 O H CHaCHOHaO C Cf=CH2 articles of this invention. For example, the diacrylates may be prepared in a styrene solution which will be readily useful as a copolymerizable solution for the purposes of this invention. Such copolymerizable solvents are those possessing at least one terminal C=CH radical. In addition to styrene, diallyl phthalate and ethylene glycol dimethacrylate have been found to be useful solvents for the'preparation of the present diacrylates directly in a copolymerizable medium.

COPOLYMERI ZABLE MONOMER Suitable copolymerizable monomers for the present diacrylates include those having at least one terminal C=GH radical. The copolymerizable monomers include styrene, vinyl toluene, divinyl benzene, ethylene glycol dimethacrylate, ethyl acrylate, methyl acrylate,

methyl methacrylate, ethyl methacrylate, other alkyl and aryl acrylates, diallyl phthalate, diallyl isophthalate, triallyl cyanurate, triallyl isocyanurate, and the like. The copolymerizable monomer might also be another one of the diacrylates of this invention, i.e., wherein the value of erizable monomer, there is usually a precise proportion for achieving optimum values of desired properties. The optimum can readily be determined for each application within the general range of 5 to 50 percent by weight.

CURING CATALYSTS The present diacrylates readily homopolymerize and readily form copolymers with monomers having at least one terminal C=CH radical in the presence of a suitable addition polymerization initiator, i.e., those which are useful in initiating polymerization of monomers having terminal C=CH radicals. Such addition polymerization initiators typically include the well-known peroxy catalysts such as benzoyl peroxide, tertiary butyl peroxide, cumene hydroperoxide, tertiary butyl perbenzoate, tertiary butyl hydroperoxide, dicumyl peroxide, and the like. The catalyst is used in sufiicient quantity to achieve the desired gel and cure cyclesfor the particular application under consideration. Catalyst selection and specification is carried out in accordance with the well-developed technology of addition-polymerization catalysis. However, the catalyst usually is provided in amounts from about 0.1 to 3.0 percent by weight of the thermosetting resinous ingredients.

REINFORCING FIBERS The precise nature of the reinforcing fibers will depend to some extent upon the nature of the product which is desired. Randomly arranged'glass fibers in the form of mats and pads have been utilized in matched-metal mold fabrications and in the preparation of laminated articles and hand lay-up and spray-up fabrications. Woven glass fiber fabrics have been utilized in the fabrication of laminated articles with the present thermosetting resinous compositions. Glass filament bundles have been utilized in the fabrication of slot sticks. Glass fiber tapes and roving's have been utilized.

In some instances the present thermosetting resinous compositions are applied to the fibers as an impregnant. To accomplish the impregnation, the fibers, customarily arranged in individual oriented strands or individual'r'nultistrand threads, are drawn through a solvent-solution of the present thermosetting resinous composition. The 'viscosity of the solvent-solution is maintained at a level which assures retention of a desired weight of the solution on the fibers as a coating or impregnant. The solutionmoistened fibers are dried to vaporize the inert solvent and leave behind an impregnation or coating of the present thermosetting resinous composition in a substantially tack-free or only slightly tacky condition. Customarily suflicient polymerization catalyst is included with the resinous solution to effect a resin cure when suflicient heat is applied to the impregnated fibers. The fibers thereafter may be applied to a desired article, and, upon heating of the article, a cure of the thermosetting resinous composition is achieved.

PRE-MIXES The designation pre-rnix is applied in the plastics industry to reinforced molding compounds which comprise various filler materials and a suitable resinous substance. The filler materials may be organic or inorganic, but customarily include such materials as asbestos, mica,

quartz, silica, glass flakes, diatomaceous earth, clay, calcium silicate, calcium carbonate and other minerals, graphite, carbon black and other materials. The pre-mixes of this invention include typical filler substances with the diacrylates herein described.

POST-CURE HEATING A feature of this invention is the discovery that the present thermoset resinous compositions possessthe ability to resist thermal deterioration resulting from exposure to elevated temperatures from about 150 to 500 F. The present resinous compositions, or course, are subjected to slightly elevated temperatures during their cure. In fact, application of heat is the cause of curing of the present resinous compositions in some applications.

We have found that these present thermoset resinous articles inherently resist severe thermal degradation. We have further found that their resistance to thermal degradation may be greatly increased by deliberate post-cure heating for selected periods of time at step-wise increased temperatures which are sequentially above the actual cure temperatures of the articles. A post-cure heating at a temperature which is (a) above 150 F. and (b) also above the cure temperature, for a period of at least one hour will increase the resistance of the articles to thermal degradation in the range of 150 to 500 F.

In some instances, the cured article may be introduced directly after its cure to an actual operating environment wherein elevated temperatures are presented which themselves provide inherent post-cure as specified, i.e., above 150 F. and above the curing temperature for at least one hour. For example, armature slot-sticks, immediately after cure, may be installed into an electrical armature which will be subsequently placed into its operating environrnent. When the armature is thereafter placed in use, the elevated temperatures thereby generated will be sufficient to achieve the needed post-cure heating directly.

Where feasible, a deliberate post-cure heating of the cured resinous composition will increase the resistance to thermal degradation.

Typical and recommended post-cure heating regime might involve:

Heat for one hour at 150 C. (302 F.);

then heat for one hour at 175 C. (348 F.); then beat for one hour at 200 C. (392 F.); then heat for one hour at 220 C. (428 F.); then heat for one hour at 230 C. (446 F.); then heat for one hour at 240 C. (464 F.); then heat for one hour at 250 C. (482 F.); and heat for one hour at 260 C. (500 F.).

Cured thermoset articles comprising the present diacrylate resinous compositions, if post-cured heated in gradual stepwise exposures of increasing temperature, will develop remarkable heat shock resistance and will retain remarkable physical strength at the elevatedtemperatures.

Typical curing regimes for the present thermosetting resinous compositions involve gel-forming at about 70 to 90 F. followed by curing at 180 to 250 F. These temperatures are typical of the curing regimes for unsaturated polyesters in the presence of typical peroxy type addition-polymerization initiators.

EXAMPLES Examples 1, 2 and 3 hereafter describe the preparation of various diacrylates according to this invention along with homopolymerization and copolymerization of such diacrylates. The diglycidyl ether of Bisphenol-A in 75 Examples 1 and 2 is sold by Dow Chemical Company under the designation DER-332 and comprises essentially In Example 3, the designation Epon refers to epoxy resins (i.e., polyglycidyl ethers of Bisphenol-A) sold by Shell Chemical Company.

Example 1.One mol DER-332 (346 g.), two mols acrylic acid (144 g.), one wt. percent triethylamine (4.9 g.) and 2.5 millimols toluhydroquinone (0.310 g.) were mixed and heated at C. for two hours and then at C. for four hours until the acid number dropped to 3.7 indicating about 98 percent conversion of the reactants to di(3-acryloxy 2-hydroxypropyl) ether of Bisphenol-A.

The product was diluted with styrene to form .a solution containing thirty parts by weight styrene. The solution had a viscosity of 550 cps. at 25 C. Addition of a polymerization initiator to the styrene solution formed a gel in 20 minutes and developed a Barcol hardness of 25-30 in the resulting thermoset copolymer.

Example 2.-Two mols methacrylic acid (172 g.), one percent by weight triethylamine and 600 p.p.m. by weight of p-quinone were mixed and heated to C. One mol of DER-332 (346 g.) was added to the heated mixture dropwise over a period of one hour while the temperature was maintained at 125-130 C. The final acid number was less than 1, indicating virtual complete elimination of the epoxy groups from the DER-332. The syrupy product was di(3-methacryloxy Z-hydroxypropyl) ether of BisphenolA.

Example 3.Two mols of methacrylic acid were reacted with two mols of various polyglycidyl ethers of Bisphenol-A.

ACID AND VARIOUS COMME ROIALLY AVAILABLE POLY- GLYOIDYL ETHE RS OF BISPHENOL-A Run Polyglycldyl Value Final Color of N o. Ether of Bisof 'n Acid Product phenol-A N0.

13 Dark Brown.

1. 9 Amber. 2. 9 Dark Brown. 5. 9 ber. 6 D0. 6. 9 Do.

The product of Run A was diluted with styrene (20 percent styrene by weight) to a viscosity of 1650 cps. The diluted mixture cured to a clear casting with 1 percent by weight benzoyl peroxide to a Barcol hardness of 35-40.

The product of Run B was diluted with styrene (30 percent styrene by weight) to a viscosity of 320 cps. The mixture cured to a clear casting with 1 percent by weight benzoyl peroxide to a Barcol hardness of 25-30.

The product of Run C was diluted with styrene (30 percent styrene by weight) to a viscosity of 3640 cps. The mixture cured to a clear casting with 1 percent by weight benzoyl peroxide to a Barcol hardness of 24-25.

Weight benzoyl peroxide to a Barcol hardness of 25-30.

The product of Run F was diluted with styrene (50 properties of the initial castings and the exposed castings Were measured and are set forth in the following Table IV.

TABLE IV.PHYSICAL PROPERTIES OF CLEAR GASTINGS -OF CURED COPOLYMERS OF 70 PARTS BY WEIGHT OF THE DIACRYLATE OF EXAMPLE 2 AND 30 PARTS BY WEIGHT STYRENE percent styrene by weight) to a v scosity of 49,000 cps. Flex m 31 Flexuml Baron, The mixture cured to a clear casting with 1 percent by Strength, Modulus) Hardness weight benzoyl peroxide.

A diacrylate as described in Example 2 was mixed lnitialvfilues 19,740 -479 3 with various copolymerizable monomers having a termi- REAGENT 57 Nitric Acid 16,700 V 0. 45s 42 nal C CH radrcaLThe binary mixtures were cured sulfuric 15, 400 446 3H0 wlth peroxy catalysts to yield clear castings. The physical 15% Hydrochloric Acid 0. 440 42:23 properties of the clear castings were evaluated. A homog f figgfigfg 13;;33 312% gig 10'7 SodiumH droxlde 2,000 0.329 26-32 polymer of the diacrylate also was cured to a clear cast 15 525% Bleach (gmocn- 18,900 0447 3H2 ing for comparison purposes. The physical properties of the cured clear castings are set forth in the following Table II.

Study .of Table IV reveals that the present copolymers resist deterioration resulting from combined thermal and TABLE II.PHYSICAL PROPERTIES OF CASTINGS P REPARED FROM THE DIACRYLATE OF EXAMPLE 2 AND VARIOUS COPOLYMERIZABLE MONOMERS Barcol Tensile Tensile Flexural Flexural Heat IZOD Copolymerizable Monomer Hardness Strength, Modulus, Strength, Modulus, Distortion Impact,

p.s.i. p.s.i. 10 p.s.i. p.s.i. 1() Point, C. ftJlbs.

None, homopolymer 43 4, 840 0. 528 19, 195 0. 495 Styrene, 2 45 8, 548 0. 488 19, 000 0. 505 Styrene, 30% 8, 326 0. 409 19, 746 0. 479 Styrene, 38 9, 545 0. 463 19, 390 0. 439 Methyl methacrylate, 10% 45 600 0. 432 12, 00 0. 80 Methyl methacrylate, 25% 48 11, 650 0. 943 21, 500 0. 618 Methyl methacrylate, 50 48 13, 400 0.844 19, 170 0. 575 Ethylene glycol dimethacrylate, 10% 50 7, 500 1. 180 15,025 0. 504 Ethylene glycol dimethacrylate, 2o% 51 6, 670 0. 926 16, 620 0. 615 Ethylene glycol dimethacrylate, 50% 55 8, 245 0. 576 Diallyl Phthalate, 25% 49 13, 320 0. 842 16, 650 0. 601 127 Triallyl cyanurate, 25% 54 12, 330 1. 166 16,110 0. 682 145 All of the thermoset cured resinous compositions in Table II were evaluated by ASTM Test D790-59T to determine fiexural properties; by ASTM Test D638-58T to determine tensile properties.

RESISTANCE TO CHEMICALS AND SOLVENTS Clear castings of the present cured resinous compositions were exposed to various common solvents at the boiling temperature of each solvent for two weeks. Thereafter certain physical properties of the exposed castings were measured. The selected castings were (A) a homopolymer of the diacrylate of Example 2 and (B) a copolymer of ninety parts by Weight of the diacrylate of Example 2 and ten parts by weight styrene. The properties of the initial and exposed castings are set forth in the following Table III.

chemical exposure at 210 F. for two months. The values of flexural strength are at least 60 percent of the original values except where the chemical was 10 percent sodium hydroxide. However the five percent sodium hydroxide solution had virtually insignificant etfect on thefiexural strength of the castings.

40 GLASS FABRIC LAMINATES 45 Example 2 and twenty percent styrene (identified as Specimen B). In each instance the laminate contained twelve plies of glass fiber fabric. The laminates were prepared by dipping the glass fiber fabric into acetone solutions of the TABLE III.PHYSICAL PROPERTIES OF CLEAR 'CASTINGS AFTER BOILING IN VARIOUS SOLVENTS FOR TWO WEEKS Homopolymer 01' the Diacrylate of Example 2 Copolymer oi the diacrylate of Example 2 Solvent (parts) and Styrene (10parts) Boiling Temp., C .Flexural Flex-oral Barcol Flexural Flexural Bareol Strength, Modulus Hardness Strength, Modulus, Hardness p.s;i. p.s.i. X10 p.s.i. p.s.l. X10

Initial Values 14, 260 0. 650 7 14, 050 0. 587 42 Solvent:

T0111 e 111 13, 825 0. 516 44 11, 245 0. 390 22 Trichloroethylene-.. 87 14, 0. 508 43 16, 305 0. 605 51 Kerosene 192 10, 950 0. 546 51 1'5, 650 0 579 45 Diesel fuel 215 15, 180 0,605 50 17, 0 574 46 Gasoline (no lead) 100 15, 200 0.591 51 19, 625 0 603 49 Gasoline (leaded)--- 75 12, 800 0. 538 53 15, 600 0 555 54 ASTM 011 No. 2---- 122 11, 390 0. 602 52 11, 075 0. 614 52 Turbo Fuel No. 4-.- 112 16, 000 0. 603 50 13, 415 0. 561 53 n-Heptane 98 18, 835 0. 603 52 10, 440 0.545 52 J 1 -4 Fuel- .128 13,670 0. 546 '52 9,960 0. 558 52 It will be observed from a study of Table III that the present copolymers and homopolymers exhibit greater resistanceto thermal exposure even in the presence of common solvents. The fiexural strength, flexural modulus and Barcol hardness values retained at least 70 percent of their 7 initial value in allreported instances. In some instances, the values of those properties actually increased as a re sult of the post-cure heating.

Various clear thermoset castings of the present resinous compositions were exposed to various common chemicals at 210 F. for two months. Thereafter certain physical resins and, after air-drying, compressing twelve plies of 65 the coated fabric between two heated plates at about 250 C. for 2.5 minutes to achieve the desired resin curing.

The flexural strength and fiexural modulus were measured according to ASTM Test D790-59T for the initial laminates. The laminates then were post-cure heated at 70 150C. for one hour; at C. for one hour,- at C.

properties of the exposed castings were measured. The 75 500 F. Other specimens were boiled in water for two hours and the fiexural strength measured after the boiled specimens and cooled to room temperature. Further specimeus were heated at 200 C. in an oven for thirty days and their flexural strength was measured at room temperature after cooling. The results of these laminates tests are set forth in the following Table V.

at room temperature and at 180 C. Specimens were postcure heated at 220 C. for 500 hours and the same physical properties were measured at room temperature and at 180 C. The results are set forth in thefollowing Table VI. I

' TABLE VL-PHYSICAL-PROPERTIES OF LAMINATE ARTICLES FORMED IN MATCHED METAL MOLDS FROM THE PRESENT RESINOUS COMPOSITIONS AND GLASS FIBER MATS Flexural Tensile Specimen Strength, Modulus, Strength, Modulus p.s.1. p.s.1. 10 p.s.i. p.s.i. 10

Tests at Boom Temperature:

Laminates (no post-cure heating) 32, 100 1, 820 17, 570 1. 550 After 200 hrs. post-cure heating at 220 G 26, 300 1, 392 13, 750 1. 285 After 500 hrs. post-cure heating at 220 C 18, 100 1, 282 9, 900 1. 250 Tests at 180 0.:

Laminates (no post-cure heating) 8, 580 0. 642 After 200 hrs. post-cure heating at 200 C... 15, 700 0. 763 After 500 hrs. post'cure heating at 220 C- 16, 900 0. 965

TABLE V.-FLEXURAL STRENGTH OF GLASS FABRIC It should be observed that 84 percent of the initial fiexural strength of both laminates is retained after two hours boiling in water. Similarly 85 and 88 percent of the initial strength is retained after 200 C. exposure for thirty days. More than 35 percent of the initial flexural strength is exhibited at 500 F. after 192 hours exposure to temperatures of 500 F. Note that the fiexural strength was measured at 500 F. indicating the actual strength which is available in the environment.

GLASS FIBER MAT LAMINATES A curable copolymerizable resinous composition was prepared with the diacrylate of Example 2 dissolved in percent by weight styrene. Seventy parts by weight of the styrene solution were mixed with parts by weight of calcium carbonate as a filler. One percent tert-butyl perbenzoate (based on the weight of resinous materials) was added as a polymerization initiator. The composition was applied to glass fiber mats in a matched-metal mold to form a laminate. Four glassfiber mats were used, each having 1.5 ounces of glass fiber per square foot of mat surface. The four mats were arranged one-atop-another as a four-layer sandwich assembly. A sufficient quantity of the resinous composition was used to prepare a laminate which comprised about percent glass fiber. The laminate was cured between the heated plates of the mold for ten minutes at265 F. under'a pressure of 200 psi. The cured article was a flat sheet, three feet wide by four feet long and about one-eighth-inch thickj It will be observed from Table VI that the elevated temperature flexural strength of the laminates increases significantly with post-cure heating treatment when that property is measured at an elevated temperature (180 C.). While the absolute value of the flexural strength appears to diminish (if measured at room temperature), yet the absolute value of the fiexural strength and flexural modulus actually increases if that property is measured at an elevated temperature.

BANDING TAPES impregnated banding tapes were prepared from the following resinous composition in solution:

The resinous solution is applied as a coating to plural multi-filament glass fiber strings which are drawn through a bath of the resinous solution and brought together to form a parallel-strand tape (free of crossing strands) which is dried to evaporate the toluene and ethyl alcohol solvents. The dried, resin-impregnated banding tape is spooled and used subsequently to Wrap electrical armatures. The wrapped armatures are preferably baked to effect a cure of the impregnated resinous composition and subsequently post-cure heated to achieve the desired thermal resistance. The banding tape serves in place of steel wire bands on the armatures of the prior art.

' HIGH MOLECULAR WEIGHT DIACRYLATES Diacrylates having values of 21 greater than one in the following generalized formula are of particular interest as will be hereinafter described.

Flexural and tensile strength and flerrural and tensile modulus were measured without postcure heating, both at room temperature and at 180 C. Specimens were postcure heated in accordance with this invention at 220 C.

wherein R is a substituent selected from the class consisting of hydrogen, methyl and ethyl radicals and n is an integer. Where n has a value greater than 1, the polymerizable resinous diacrylate can be handled only for 200 hours and the same properties were measured in a solvent. The solvent may be inert or may be copolymerizable with; the diacrylate. The resin will be prepared by reacting in the presence of a suitable catalyst such as triethylam-ine, a monocarboxylic acid having the formula 032 ii OH R with a polyglycidyl ether of Bisphenol-A:

where n is an integer greater than one and less than twenty. The high molecular Weight resin has a molecular weight in the range from about 800 to 8000, and preferably from about 1000 to 3000. These materials can be impregnated upon various materials from their solution in volatile solventssuch as acetone. The materials as impregnants are nearly dry to the touch, i.e., they are non-tacky. Preferably a suitable polymerization initiator such as benzoyl peroxide is combined with the high molecular weight resins for conjoint impregnation upon glass fiber tapes and mats. The storage life of such catalyzed, impregnated fibrous materials is commercially feasible; storage life of such catalyzed materials has exceeded one year in some instances.

These high molecular weight resins moreover are of especial interest where excellent chemical resistance is required at elevated temperatures.

A specimen of the present high molecular Weight resin was prepared from methacrylic acid and a polyglycidyl ether of Bisphenol-A having a value of n of about 2.0 to 2.1. The resulting diacrylate resin can be diluted with 50 percent styrene to produce a copolymerizable composition having a viscosity of about 500 cps. at 77 F. The styrene copolymers are readily cured, for example, with benzoyl peroxide as initator. The cured copolymers exhibit a Barcol hardness of 37, a heat distortion point (264 p.s.i.) of 101 C., a flexural strength of 19,475 psi. and a flexural modulus of 0.493 p.s.i. Clear casting specimens were placed in beakers containing common chemicals at 210 F. for two months. The thermal exposure is, within the intent of this invention, a post-cure heat treatment which serves to increase the resistance of these cured copolymers to thermal degradation. The flexural strength and flexural modulus of the specimens was measured after the extended chemical exposure. The results are set forth in the following Table VII. 7

TABLE VII.PHYSICAL PROPERTIES OF CLEAR CAST- INGS OF HIGH MOLECULAR WEIGHT DIACRYLATES AND STYRENE COPOLYMERS (CONTAINING 45% BY WEIGHT STYRENE) Flexural Flexural Reagent Strength, Modulus,

p.s.i. p.s.i. 10-

None (initial values) 19, 475 0. 493 5% nitric acid 6, 020 0. 470 25% sulfuric acid 16, 725 0. 477 hydrochloric acid 13, 000 0. 479 acetic acid 6, 250 0. 392 5.25% bleach (NaOCl) 16, 000 0. 502 5% sodium hydroxide 19, 650 0. 483 10% sodium hydroxide- 19, 080 0. 479

In all instances reported in Table VII, the specimens were tested in the wet condition immediately after removal from the beakers containing the chemicals. If the specimens were permitted to dry and recover from the exposure for about eight hours, the flexural strength and moduli values usually increase.

From inspect-ion of Table VII, it is of interest to note that remarkable retention of physical properties is evidenced after exposure to sodium hydroxide solutions. The present thermoset copolymers retain virtually all their flexural strength after extensive exposure to boiling caustic solutions. The flexural moduli are only slightly diminished. Further tests have been carried out to demonstrate the remarkable resistance of these high molecular weight diacrylate copolymers to alkaline deterioration at elevated temperatures.

The effect of post-cure heating treatments on the co- @o-n-omdshm polymers of high molecular weight diacrylates (as just described) is exhibited from three specimens as follows:

First specimen.The copolymerizable composition just described (45 Weight percent styrene and 55 weight percent of the methacrylic acid ester of polyglycidyl ether of Bisphenol-A having a value of n from 2.0 to 2.1) was catalyzed with 1 percent by weight t-butyl perbenzoate. The composition gelled at 180-2l0 F. and, after cure,

was post-cure heated at 250 F. for one hour and thence at 300 F. for two hours.

Second specimen. The copolymerizable composition was cured with 1% benzoyl peroxide and 0.3% by weight of a six percent solution of cobalt naphthenate. Gelation occurred at 77 F. and the cure was completed in four days at 77 F. The castings were post-cure heated at C. (248 F.) for one hour and-then at C. (302 F.) for two hours.

Third specimen-The copolymerizable composition was cured with 1% benzoyl peroxide and 0.3% of a six percent solution of cobalt naphthenate. Gelation was carried out at 7-7 F. and the castings cured at 77 F. in four days. There was no post-cure heat treatment. 7

All three specimens were tested for flexural strength and modulus and thereafter placed in 25% potassium hydroxide at 210 F. for a week. The specimens thereafter were cooled to room temperature in the potassium hydroxide solution, dried and immediately tested for physical properties. The flexural strength, modulus and weight increase in each instance is presented in Table VIII.

TABLE VIII.-PHYSIGAL PROPERTIES-COPOLYMERS OF 55 PARTS BY WEIGHT HIGH MOLECULAR WEIGHT DI- ACRYLATES AND 45 PARTS BY WEIGHT STYRENE Flexural Flexural Weight Specimen Strength, Modulus, Increase,

p.s.i. p.s.i. 10 percent Initial Values:

First 19, 500 0. 493 Second. 17, 600 0. 497 ird 14, 200 0. 402 After One Week in Boiling Potassium of the First Specimen. More significant, however, is the fact that the thermal exposure at 210 F. in the presence of 25 solution of potassium hydroxide actually increased the flexural strength of the Third Specimen from 14,200 to 14,800 p.s.i.

13 14 The resistance to caustic exposure of the thermoset res- Vie claim: inous compositions containing these high molecular 1. A thermoset solid article adapted for use at elevated weight diacryiates as homopolymers and as copolymers temperatures from about 150 to 500 F. comprising as has resulted in their acceptance as components of alkathe resinous component thereof a polymerized mass line batteries and fuel cells. The relative non-tackiness of formed by addition polymerization of at least one di'acrythe high molecular weight diacryla-tes prior to their cure late having the formula H R (CH3): (CHM has resulted in their gaining acceptance as a pre-preg wherein R is a substituent selected from the class conresm. 15 sis-ting of hydrogen, methyl and ethyl radicals and n is an MIXTURES OF DIACRYLATES integer from zero to twenty;

the said article after polymerization and said mass hav- The relatively high molecular weight diacrylates, i.e.,

mg been exposed to an elevated temperature which those wherein the value of n is greater than one, have been successfully blended with lower molecular weight is above its curing temperature and also is above diacrylates, i.e., those similar to the diacrylate of Ex- F-for more than 9 hourample 2 h i n i zero to yield copolymerizable m 2. A thermoset solid article adapted for use at elevated tures of diacrylates. The mixtures also readily blend with temperatures from about 150 to compl'lslng as and copolymerize with the herein-described copolymerizthe Tssillous component thereof a copolymsflled m able monomers such as styrene and the like. forward by addition polymerization of A mixture of 40 parts by weight of the diacrylate of f 95 i0 59 percent y W g of a diacrylate Example 2 was mixed with 60 parts by weight of a high having th formula molecular weight diacrylate wherein the value of n was wherein R is a substituent selected from the class about 2.0 to 2.1. Seventy parts by weight of that mixture consisting of hydrogen, methyl and ethyl radicals was dissolved in thirty parts by weight styrene to yield and n is an integer from zero to twenty; and a copolymerizable resinous composition. The composi- (b) from about 5 to 50 percent by weight of at least tion cured readily with the peroxy polymerization initiaone copolymerizable monomer having at least one tors. The clear castings, without post-cure heat treatment, terminal C H radical, exhibited a flexural strength of 15,750 p.s.i., a flexural the said solid article after polymerization of said mass modulus of 0.475 and a Barcol hardness value of 41. having been exposed to an elevated temperature These clear castings were exposed to common solvents at which is above its curing temperature and also is their boiling temperatures for two weeks. After the solabove 150 F. for more than one hour. vent exposure, the castings were allowed to cool to room 3. A thermoset solid article adapted for use at eletemperature in the solvent and thereafter were removed vated temperatures from about 150 to 500 F. comprisfirom the solvent and immediately tested for physical ing fibrous reinforcing elements embedded within a cured properties. thermoset resinous composition comprising a polymerized The solvents included gasoline (lead-containing) mass formed by addition copolymerization of ASTM Oil #1, Turbo Fuel #4 and n-heptane. The re- (a) from 95 to 50 weight percent of a diacrylate havsults of the tests are set forth in the following Table 1X. ing the formula TABLE IX.FLEXURAL PROPERTIES OF MIXED DIAO' RYLATES AND STYRENE OOPOLYMERIZED CAST- INGS AFTER TWO WEEKS EXPOSURE To COMMON SOLVENTS AT BOILING TEMPERATURES wherein R is a substituent selected fro l s Solvent and Boiling Flexural Flexural Barcol m the c a 8 Temperature Strength, Modulus Hardness consisting of hydrogen, methyl and ethyl radicals,

P- P -X and n is an integer from zero to twenty; and

None (initial Values) 15,750 0,475 41 (b) about 5 to 50 percent by weight of at least one fio llead eoi ta g osl 22, 400 (L538 47 copolymenzable monomer having a terminal $1i119ti35131ll36flfl 338 8.233 2(15 lI l1? :f1i (1 l after copolymerization of said 20300 0'514 46 mass having been exposed to an elevated tem- Note in the instances reported in Table D(, the flexural 7 perature which is above its curing temperature strength and modulus of the castings actually increased and also is above F. for at least one hour. after exposure to common solvents at their boiling tem- 4. Alaminated article comprising glass fibers embedded peratures, indicating that the elevated temperature solvent within a cured thermoset resinous composition compris exposure served as a post-cure heat treatment in according a copolymerized mass forms-x1 by addition polymeriance with this invention. 7 zation of 15 16 (a) from 95 to 50 percent by weight of a diacrylate 6. A method of preparing an electrical laminate comhaving the formula. prising ii i 032: ooon'iononiooo-[omonomo@oQo-p-omoncnmco=crn R (H l (5H i 011 R wherein R is a substituent selected from the class (1) compressing a resinous mixture with fibrous reinconsisting of hydrogen, methyl and ethyl radicals forcing materials in the presence of an addition and n is an integer from zero to twenty; and polymerization initiator capable of causing addition (b) about 50 to 50 percent by weight of at least one polymerization between C=CH radicals to effect copolymerizable monomer having a terminal a thermoset cure of the said resinous mixture; C=- -CH radical; (2) recovering a solid, thermoset resinous article havsaid laminated article after copolymerization of ing the said reinforcing materials embedded therein;

said mass having been exposed to an elevated (3) post-cure heating the said thermoset resinous. temperature which is above its curing temperaarticle at a temperature which is above the curing ture and also is above 150 F. for more than temperature and also is above 150 F. for a period one hour. greater than one hour whereby the post-cure heated 5. A fibrous impregnating composition comprising a article resists severe reduction in flexural strength solution of polymerizable resinous material substantially and reduction in flexural modulus at elevated temfree of unreacted epoxy radicals comprising, in an inert peratures in the range of 150 to 500 F.; volatile solvent, at least one diacrylate having the forwherein the said resinous mixture includes (a) mula G i 0m= 1iioonionomoooornenoniooo noniononzooe=o1n R OH i OH OH R (CH3): (CH3):

wherein R is a substituent selected from the class confrom 95 to 50 percentby weight of a diacrylate having the formula 0 ii bm=ocrnonomoo O[CH2(|3HCH2OC o- ..onionomooc i=cni R OH i OH OH R ah H92 sisting of hydrogen, methyl and ethyl radicals and 11 wherein R is a substituent selected from the class consisting of hydrogen, methyl and ethyl is an integer from one to twenty;

and a polymerization-initiating quantity from 0.1 to radicals and n is an integer from Zero to twenty;

u and V 3.0 percent by weight of an addrtron polymerization (b) $1.0m 5 to Percent by weight of at least one initiator capable of causing addition polymerization copolymerizable monamgr having at least between -@OH radicals at elevated temperatures. 49 terminal C=CH radical.

References Cited UNITED STATES PATENTS 2,331,265 10/1943 Coleman et al. 260--486 X 2,359,622 10/1944 Coleman et a1. 260486 X 2,575,440 11/1951 Bradley 260486 X 2,604,464 7/1952 Segall et al. 260-47 2,859,199 11/1958 Parker 260835 3,067,222 12/1962 Anderson 260486 3,156,580 11/1964 Howard 117-75 2,784,128 5/1957 Schroeder 260 -837 X 2,824,851 2/1958 Hall 260- 837 3,066,112 11/1962 Bowen 260-47 X EARL M. BERGERT, Primary Examiner.

HAROLD ANSHER, Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,373 ,075 March 12 1%5 Frank Fekete et :11.

It is hereby certified that error appears in the above numbered patent. requiring correction and that the said Letters Patent should read as corrected below.

Cgll mns 3 and 4 lines 9 to 14 the formula should appear as shown e 0w:

0 CH CH H ci 0- -cn cncn o c o -CH2CH H2 Columns 5 and 6, lines 38 to 40, the formula should appear as shown below O C OCH CHCH (CH3) 2 (CH3) 2 Columns 9 and 10, TABLE VI, first column, line 7 thereof, "200 C." should read 220 C. same table,third column, line 1, Z and 3 thereof, "1,820" "1,392" and "1,282" should read l .820 l 392 and l 282 Column 14 line 24 "forward" should read formed lines 40 and 67,

C=H each occurrence, should read C=CH Columns 13 and 14, lines 52 to 54, the formula should appear as shown below:

0 I cu =ogocH cncu o c Q 0- ---CH cncu o@ 0 Q o R on I on I -CH CHCH OCC=CH R OH Column 15, line 12, "50 to 50" should read 5 to S0 lines 25 to 28, that portion of the formula reading j 0 CH =C OCH should read CH =CCOCH Signed and sealed this 23rd day of September 1969.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Parents 

4. A LAMINATED ARTICLE COMPRISING GLASS FIBERS EMBEDDED WITHIN A CURED THERMOSET RESINOUS COMPOSITION COMPRISING A COPOLYMERIZED MASS FORMED BY ADDITION POLYMERIZATION OF (A) FROM 95 TO 50 PERCENT BY WEIGHT OF A DIACRYLATE HAVING THE FORMULA 